[test-utils] Give a little hint about running CockroachDB on test fai…

…lures (#5125)

This is a pattern I use a lot, but I want to help make it more visible
to folks during test failures.

Digging into the state of Cockroach after a test failure is a useful
debugging tool, so I want to make
it obvious "how to do that".

test-utils/src/dev/db.rs

@@ -640,8 +640,13 @@ impl Drop for CockroachInstance {
                 // Do NOT clean up the temporary directory in this case.
                 let path = temp_dir.into_path();
                 eprintln!(
-                    "WARN: temporary directory leaked: {}",
-                    path.display()
+                    "WARN: temporary directory leaked: {path:?}\n\
+                     \tIf you would like to access the database for debugging, run the following:\n\n\
+                     \t# Run the database\n\
+                     \tcargo run --bin omicron-dev db-run --no-populate --store-dir {data_path:?}\n\
+                     \t# Access the database. Note the port may change if you run multiple databases.\n\
+                     \tcockroach sql --host=localhost:32221 --insecure",
+                     data_path = path.join("data"),
                 );
             }
         }